Two or more events that occur at the same time.
In the video below, we can see that the letter R (a "sprite" as it's called in Scratch) is coded to change size, then colour, and finally rotate in sequence; one change after the other.
In grade 2, students learn to write code with concurrent events where two or more outputs are occurring at the same time. The video below now shows the R sprite rotating and changing colour at the same time. Other examples of concurrent events might have multiple sprites with multiple outputs occurring at the same time. This example corresponds with Mathematics Grade 2 C3.1.